Multiple prime mover control and synchronization



G. F. DRAKE Dec. 2, 1947.

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MULTIPLE PRIME MOVER CONTROL AND SYNCHRONIZATION Filed March 10, 1944 5Sheets-Sheet 5 V i N V BN 'O Geo/ye 6701726! Drake Mia a .4

TTO AQYJ new Dec. 2, 1947 UNITED STATES. PATENT OFFICE MULTIPLE PRIMEMOVER CONTROL AND SYNCHRONIZATION George Forrest Drake, Rockford, 111.,assignor to Woodward Governor Company, Rock1ord,1ll., a corporation ofIllinois Application March 10, 1941, Serial No. 525,913

.control system which is especially adaptable to the control ofmechanically separated power units, which permits of speed and othermanual adjustments from a remote point of control, which is very lightin weight, and which is simple in construction and reliable inoperation.

A further object is to provide a control which avoids the use of relays,brushes, slip rings, con-- tacts, or the like immediately associatedwith and subject to the vibration of the prime movers.

Another object is to provide apparatus of the above character in whichthe synchronizing control may be disabled and the speeds of theindividual power units may be changed to a preselected value.

A further object is to provide an automatic synchronizing control partof which is utilized in a novel manner in adapting the controlledengines for manual speed adjustment either in dividually or as a group.

The invention also resides in the novel manner of applying the speedcorrections and in the-construction of the individual engine speedadjusters that permits of quick changes in the engine speed settings.

Other objects and advantages of the invention will become apparent fromthe following detailed 18 Claims. (CI. 60-97) description taken inconnection with the accompanying drawings, in which Figure 1 is a,schematic view and wiring diagram of one form of the improved control.

Fig. 2 is a schematic view showing the parts of one power unit andassociated speed controller.

Fig. 3 is an elevational view of a step motor and its controlling switchused in effecting speed adjustment of the individual power units.

Fig. 4 is a view of the commutator switch shown in Fig. 3 with the partsdisposed in a different position;

Fig. 5 is an elevational view of gearing forming part of the manuallyoperable speed adjusting mechanism.

Fig. 6 is a fragmentary plan view taken substantially along the line 6-6of Fig. 5.

Fig. 7 is a section taken along the line 1+1 of Fig. 5.

Fig. 8 is a, schematic view and wiring diagram of a modified form of.the control.

Fig. 9 is afragmentary perspective view of the modified form of enginespeed adjusting mechanism.

Fig. 10 is a partial schematic view and wiring diagram of anothermodification.

While the improved control system is applicable to the control ofvarious kinds of multiple unit powergenerating systems under widelyvarying operating conditions, .it has been shown in the drawings andwill be described herein as applied to the remote control andsynchronization of a group of internal combustion engines each of whichdrives the propeller 6 of a multi-engine airplane. It is to beunderstood, however, that I do not intend to limit. the invention bysuch disclosure nor to the particular illustrated constructions of thevarious switch, speed adjuster, and motor units, but aim to cover allmodifications, alternative constructions, and uses falling within thescope of the invention as expressed in the appended claims.

For convenience, the engines are designated as A, B, C, and D in Fig. 1and B and C in Figs. 8 and 10, and the parts common to or associatedwith the respective engines are referred to as a group by referencenumerals to which letter exponents are added to indicate individualparts. For example, 6" is the propeller of engine A.

Each of the engines, whose speed is to be matched against orsynchronized with a selected reference or master speed, is equipped witha speed changer or adjuster movable to different positions to vary theoperating speed of the engine. The adjuster may take various forms andoperate through the medium of a fuel control throttle or the like.

It is shown herein as a rack bar 4 which may be moved as desired to varythe pitch of a propeller 6 driven by the engine and controlling thespeed of the latter.

In the embodiment shown in Figs. 1 and 2, the speed change is effectedthrough the intermediary of a governor 5 which operates automatically tomaintain a constant engine speed correspond ing to the setting of theadjuster 4. The governor shown is of the hydraulic type having a servomotor 1 rotatable with the propeller 3 and actuating the follower 8 of acam 9 which, through bevel gear connections, turns the propeller bladeson their longitudinal axes. In the present instance, the governorincludes a rotary head i driven in unison with the controlled engine andpivotally supporting flyballs II, the centrifugal force of which isopposed by and balanced against a compression type speeder spring i2,one end of which bears against an abutment formed by the end l3 of thespeed adjusting rack 4. The latter is slidable endwise in a guide I4formed in the governor casing ii. The other end of the spring l2 engagesthe head i6 of a control rod I! which bears against the flyball arms i8.The ball head I0 is on the upper end of a sleeve i9 journaled in thegovernor casing and driven from its lower end through a gear connection28 with the engine crankshaft 2i.

, The control rod i1 actuates a valve 22 regulating the flow of pressurefluid to and from the servo 1 so as to maintain an engine speedcorresponding to the governor speed setting. The valve includes a land23 on the rod cooperating with ports 24 in the sleeve i9 which portscommunicate with a conduit 24' constituting the outlet of a booster pump25. Oil is delivered to the pump from a branch 26 leading from theoutlet of a gear pump 21 that supplies all at low pressure to the enginelubricating system. The pressures developed by the pumps and 21 aredetermined by the setting of by-pass valves 28 and 29 The lower end ofthe valve sleeve i8 may be opened and closed according to the positionof a land 30 on the lower end of the stem i'l. Intermediate the lands 23and 30, the sleeve is ported and communicates with a conduit 3! whichleads through a suitable collector ring (not shown) to the casing 32 ofa distributor valve 33 disposed within the propeller shaft. This valveincludes a plunger 34 having lands thereon controlling the covering ofports 35 and 36 leading from the supply line 3!, ports 31 and 38communicating with the outlet of the pump 21, and ports 39,and 40respectively communicating with the head and rod ends of the servocylinder 1'. A spring 4| acts on the plunger 3| to maintain the valve inthe normal position shown.

As a result of the foregoing arrangement, the parts will be positionedas shown when the englue is operating at the speed corresponding to thegovernor speeder spring setting. An increase in engine speed raises thepilot valve member i1, uncovering the ports 24 and permitting the flowof pressure fluid to the servo motor through the ports 36 and 40. Thisforces the piston 1 outwardly thereby increasing the propeller pitch.

' Oil from the head end of the cylinder is forced back into the enginelubricating system through the ports 39 and 38. As the engine slows downto the speed determined by the governor, the pilot valve descends to theposition shown in Fig. 2, thus shutting off the supply of oil to theservo motor, the pump 25 being relieved through the valve 28. A decreasein engine speed below the governor setting results in lowering of thevalve rod, the land 30 opening the lower end of the valve chamber to thedrain. As a result, the propeller pitch is reduced. In response to theresulting pick up in engine speed, the governor raises the valve plungerand closes off the drain just as the engine reaches the set speed.

in accordance with movement of the speed adjuster or rack 4, areeffected in the present instance through a pinion 4'! on a shaft 43, thepinion meshing with teeth 44 on the exterior of the rack 4 which is inthe form of a cup. The shaft 43 is journaled in the governor casing.

Feathering of the propeller to prevent wind; milling of a disabledengine may be effected by energizing an electric motor 44' under manualcontrol to start an auxiliary pump 45 which communicates with theconduit 3i through a pipe 48 and a valve 41 normally closed by a spring48. This pump, which is supplied from the engine lubricating system,develops a substantially higher pressure than the pump 2'. Under thispressure, the cut-off valve 41 is moved to close the conduit 3] andpermit the high pressure oil to flow to the servo cylinder through thedistributor valve ports 38 and 40. This causes the servo piston to moveout through a range in which a steeper cam section 9' is effective toincrease the propeller pitch to a set maximum. With the blades thusfeathered, rotation of the engine is stopped and the blades remain atfull pitch, the motor 44 being thereafter deenergized before too high apressure has developed.

To unfeather the propeller, the motor 44 is again started and thenpermitted to operate until the pump 45 has built up a pressuresuiiicient to compress the spring 4| of the distributor valve and movethe land 4! past the .port 39. This connects the engine lubricatingsystem to the rod end of the cylinder through ports 31 and 40 and admitsthe high pressure oil to the head end of the cylinder through ports 33and 38. Movement of the piston is thus reversed to reduce the pitch ofthe blades. The unfeathered propeller is permitted to windmill to acertain speed before the motor 44 is deenergized whereupon the cut-offvalve 41 restores the cranked engine to the control of its governor 5and the spring 4! reconditions the distributor valve for normaloperation.

To adjust the individual speeds of the controlled engines, eithermanually or automatically, the speed adjuster 4 of each engine is movedin the desired direction by an electric actuator controllable from aremote point. In the present instance, the actuator canprises anelectric step motor 5| (Fig. 4) incorporated in the governor casing andincluding a stator 52 carrying three groups of windings 53, 54, and I!distributed over twelve stator teeth I defining poles a to l. Apermanent magnet rotor 51 has two salient poles with faces of such widththat they span five of the stator pole faces and coact therewith toproduce a distinct oogg ng action when the stator is deenergized. Eachcoil encloses two adjacent stator teeth and is connected in series witha similar coil that encloses one of the same teeth and the next adjacenttooth. Thus, of the four coils 53, one encloses poles a and b. a secondpoles b and c, the third polesa and h, and the fourth poles h and i. Allfour coils are in series as indicated by the full line 84. The coils 54are similarly mounted to enclose poles c, d, e, and i, k are connectedin series as indicated by the dotted line 68. The coils 55 enclose polese. f, a, and k, l. a and are connected in series as indicated by the gdot-dash line 51. To complete a delta form of wiring, one end of theconductor 48 is connected at 68- to the conductor 86, the correspondingends of the conductors 68 and 61 being connected at 65' and 61" to theconductors 61 and 68 respectively.

Changes in the speed setting of the governor By energizing the statorwindings from a direct current source selectively in various polaritycombinations, the rotor may be caused to assume twelve different welldefined angular positions and to turn progressively in either directionby varying the combinations properly. Such excitation is effected in thepresent instance by a commutator switch 58 comprising three segmentalcontacts 59 and 60 and 6| carried on the face of an insulating disk 62fast on a shaft 63 which carries rings 64 engaged by brushes 65.; Thelatter are connected by the conductors 66, 61, and 68 and, therefore, tothe windings 53, 54, and 55 of the step motor. The segments are engagedby wiper brushes 69, 10, II, and I2 angularly spaced as shown in Fig. 3and mounted on the free ends of spring arms 15 and 16. These arms of thedifferent commutating switches are arranged in pairs respectivelyconnected by conductors 13 and 14 to the positive and negative terminalsof. a direct current source such as a battery 11 (Fig. 1), manuallyoperable toggle switches 18 being included in the conductors.

When the shaft 63 is disposed as shown in Fig. 3,, the windings 55 willbe energized through the brushes 69 and I and the segment 59 while theopposite terminal of the current source will be connected to thewindings 53 through the brushes 1| and 12 and the segment 6|, thepotential drop across the conductor 68 being zero. With the deltaconnections, the windings 53 are placed directly across the line and thewindings 54 and 55 are in series across the line, and, therefore, the

current therein is half that of the coils 53. Accordingly, the fluxdensities in the different stator poles will be in the ratios of 4 forthe teeth b teeth d, f, 7', and l. The effects of the windings on theteeth e and k cancel each other, so that these teeth are deenergized andthe rotor poles are attracted by the other teeth to the well definedposition shown.

Now assume that the switch shaft 53 is advanced thirty degrees clockwiseas shown in Fig. 4, the contacts 12 and 1| respectively engage thesegments 60 and 6| thereby connecting the conductors 66 and 68 to shortout the coils 54. The flux densities in the different stator teeth arethen zero in teeth d and 7, 2 in teeth 0, e, i, and k, and 4 in teeth a,b, g, h, and i. The rotor is thus attracted to a position one-twelfth ofa revolution in' advance of that shown in the drawing. In a similarmanner, the energization ratios of the teeth will be varied in differentcombinations as the switch shaft 63 is advanced in thirty degree stepsand the rotor 51 will follow this shaft.

The torque of each step motor is amplified and the motion thereofreduced and applied to the associated speed adjuster 4v in a large ratiosuch that the speed setting of the adjuster will be .changed in a verysmall increment for each stepping movement of the step motor shaft 80.To this end, the motor torque is transmitted through gearing 8|, a shaft82, and then, in the embodiment shown in Figs. 1 and 2, through adifferential 83 to the shaft 43.

The arrangement above described reduces the motion of the step motor ina ratio of about 500 to 1 and operates to lower the rack 4 and increasethe speed setting one R. P. M. for each step of movement of the motorshaft 80 in one direction and conversely to effect a similar decrease inmotor speed as the shaft turns in the opposite direction.

Means selectively controllable from a remote point is provided forbreaking the driving connection between each step motor and theplanetary safe operation of the engine and aeroplane under' specialconditions. Actuation of the speed adjuster in this manner is effectedherein by a compression spring 81 (Fig. 2) encircling a screw when thedrive connection with the motor 5| is and h, 3 for the teeth a, c, andi, and 2 for the 86 and acting between the rack 4 and'the casing l5.This spring is strong enough 'to overcome the speeder spring I2 and movethe speed ad-- juster C in the speed-increasing direction to thepredetermined value which, as shown in Fig. 2, maybe determined by astop in the form of a screw 92. The latter threads into the governorcasing, and its end is positioned to engage the end of a rack 93 meshingwith the pinion 42 and guided in the casing. This rack moves back andforth slowlyand idly with the speed adjuster under normal operatingconditions. However,

broken, the force of the auxiliary spring 81 is applied to move theracks 4 and 93 rapidly until the stop 92 is encountered thereby changingthe governor speed setting and speeding up the engine quickly. v

The differential gearing 93 of each governor constitutes part of areleasable cluth connection for freeing the speed adjuster 4 whileproviding for reestablishment of the driving relation in the positionsto ,which the parts are moved by the spring 81. Accordingly, the sungear of the differential is carried by the shaft 82 while the planetgears are on a yoke indicated at 95 and rotatable with the shaft 43. Thering gear 96 meshing with the planet gears is formed externally withratchet teeth 94 engaged by-a pawl 91 pivoted at 98 and acting, whenengaged, to hold the ring gear against clockwise turning under thepredominating action of the spring 81. This active position of the pawlis normally maintained by a spring 99 acting on an arm |00 which isconnected to the armature |0| of a solenoid I02.

When the solenoid is energized, the pawl is retracted, thereby freeingthe ring gear for rotation under the influence'of the spring 81 untilthe rack 93 encounters the stop 92. The speed setting of the associatedengine speed adjuster is thus increased substantially instantaneously tothe value selected by adjustment of the stop 92. On deenergization ofthe solenoid, the pawl reengages the ratchet under the action of thespring 99 and the connection is'restored so that the governor settingmay again be decreased by operation of the step motor 5|. It will beobserved that the, clutch 83 is located in the driving train between thespeed reduction gearing 8| and the adjusting pinion. Thus, the spring 81always applies a torque to the ring 96 in a direction to hold the activetooth 94 against the latch 91 so that during operation of the motor 5|in the speed-increasing direction, the spring 81 effects the speedadjustment to an extent permitted by the motor operation.

' Provision is made for simultaneously energizing all of the solenoidsI02 from the remote point of control, usually a panel 3 (see Fig. 6)

' in the cockpit of the airplane, so as to enable the automaticsynchronizing control to be disabled and the speed adjusters 4 of thedifferent engines to be shifted quickly to their preselected Iaccurately to the ratio of two resistances, one of which is variable andcomprises a rheostat I00. The system is substantially unaffected byvoltage changes. The resistances are connected to the battery leads I3and I4 by conductors I" and I08. The movableelement I09 of eachrheostat' is fast on the shaft 43 of the associated governor 5, theangular position of which constitutes a reasonably accurate indicationof the prevailing speed setting of the engine in terms of which speedthe instrument I05 is calibrated. The control of the speed indicatorsfrom the governor adjusting shaft 43 is also an advantage in that thegovernor may be adjusted when its engine is idling with its throttleretarded and thus conditioned to accelerate up to a'preselected speedwhen the throttle is advanced.

Means is provided for establishing a' master or reference speed which isadjustable selectively and against which the speeds of the slave primemovers are matched and brought into synchronism. This reference speed isprovided by a power driven unit which may comprise one of the engine(for example, the engine B, Fig. 1) whose speeds are to be synchronizedor a separate smaller motor H (Fig. 8) preferably electrically driven.In each instance, the master power unit drives a device capable ofdelivering electrical energyvarying in character according to selectedchanges in the reference speed. Herein, it comprises a generator IIIhaving its shaft H2 mechanically connected to the master power unit andpreferably of the permanent magnet type such, for example; as is shownin Patent No. 2,071,536. It will be apparent that the frequency of thegenerator output will change directly with changes in the speed of themaster power unit. Similar generators H4, II4, and H4 are mounted on anddriven by the slave engines A,

C, and D. These .provide alternating current sources whose frequenciescorrespond to the prevailing speeds of the respective slave engines.

The speed of each slave engine is compared with the master referencespeed by a differential mechanism which may take various forms. In theform shown in Fig. 1, the differentials are of the electrical typecomprising three-phase differential motors H5, H5 and H5 assigned to therespective slave engines A, C, and'D and preferably mounted side by sidein a box behind the control panel H3. Each differential motorcomprises'a three-phase two pole stator having a winding H6 and athree-phase two pole winding H! on the rotor which is fast on a shaftI22 coupled directly to the shaft 63 of the commutator switch 58 of thecorresponding slave engine.

One winding of each differential H5, in this 8 actly matches the masteror reference speed, the relation of the currents in the windings H3 andIII will be same, and there will be no mechanical movement of the rotorshaft I22 of the differential motor H5.

When the speeds of the master and one controlled engine are different,the frequencies of the currents supplied by the respective generatorswill differ proportionately and the differential rotor shaft will turnat a rate'proportional to this difference and in a direction determinedby which frequency is the higher.

evidenced by matching of the Thus, in the case of the control shown inFig. 1, if the speed of one of the controlled engines, for example A,differs from that of the master engine B, the differential motor H5"will actuate the commutator switch 58 causing the step motor 5I to turnin a direction to adjust the controlled engine governor 5' and correctfor the speed difference. Such automatic adjustment continues until thespeed of the engine A again coincides with that of the master engine asfrequencies of the alternators III and H4".

It will be observed that by closing the switch I04, the clutch releasemagnets I02 on all of the engines will be energized and the automaticsynchronizing control be disabled, the speed adjusters of all of theengines being shifted quickly to the predetermined speed settingspreviously described.

Provision is made for disabling the automatic synchronizing control andfor manually changing the speed setting of governors 5 either alone orin unison from remote points of control on the panel I I3. To disablethe differential motors H5, the movable contacts of the switches I I3and I 2i are carried by a common actuating element I23 which isconnected to the armature I24 of a solenoid having a winding I25. Whenthis wind-- gized in response to closure of the push button switch I21at a time when the switches I0 and I29 are closed and the mechanismconditioned for automatic control.

Movement ofthe switch element I23 to close the switches H9 and I2I whenthe relay is energized also closes a switch I30 to establish a sealingcircuit for holding the winding energized. This circuit extends from thebattery through the conductor I3, the winding I25, a conductor I3I,normally closed switches I32 and I33, the holding switch I30, aconductor I34, a conductor I 20. and the switch I8. The switch I33 isopened by depression of a manually controllable push button on the panelH3 to break the holding circuit for the solenoid and disable theautomatic control.

The switch I32 is arranged to be opened by depression of a push buttonI35 which closes the switch I04 for energizing the magnets I 02 of thevarious engines to provide the emergency speed up previously described.The actuators for the switches I04, I 33, and I2! are located on thecontrol panel I I 3.

The forward end of each differential motor increased or decreased asdesired, most of the partsof the. automatic synchronizing control beingutilized in providing for such manual adjustment.

Simultaneous manual adjustment of all or any number of the engine speedadjusters 4 is effected by engaging clutches to connect the gears I38and then turning one of the hand wheels I40. In the present instance,the clutches include gears I4I rotatable on the inner ends of shafts I42and having knobs I43 which project from the front of the panel 3 andbywhich the shaft may be shifted axially between two positions maintainedby a detent (not shown) which coacts with grooves I 44 in the shaft.When each knob I 43 is pulled forwardly, the gear I is moved into meshwith two idler gears I45 constantly meshing with the gears I38 onopposite sides of the gear I. The adjacent gears I are thus connected.The gear clutches may be disengaged simply by pushing the knob inwardlyto the position shown in Fig. 6.

When all three of the knobs I43 are retracted, all of the gears I38 andthe differential motor shafts I22 and the shafts I39 will beinterconnected. Then, by turning any one of the hand wheels I40, all ofthe commutator switches 58 tial, sufiiciently accurate control of theengine will be turned in the same direction and the step motors 5|operated to effect equal changes in the speed settings of the governors5. The switch I29 controlling the circuit of the solenoid I25 isactuated by movement of one of the knobs I 43, being closed normallywhen the knob is pushed inwardly. When the knob is retracted preparatoryto manually changing the engine speeds, the switch is'opened therebydeenergizing the winding I25 to disable the automatic control.

Operation of the entire system above described in a multi-motoredairplane would be somewhat as follows: First, assume that the control isconditioned for manual operation, that is, the line switch 18 is closedto render the indicators I05 operative, and that the knobs I43 arepushed inwardly to disengage the associated gear clutches. With theengines running idly and their throttles retarded, the hand wheels. I40would be turned individually until the indicators I05 show take-offspeed. When ready for the take-oil, the throttles (not shown) for thedifferent engines are advanced and the engines will 'all come up to thespeeds for which their governors are set.

After the take-off, the knobs I43 will be pulled forwardly and thegovernor speed settings decreased simultaneously to the desired cruisingspeed. Then, the clutches will be disengaged by pressing in the knobsI43 and the automatic control will be rendered operative by closing theswitch I21 to energize the winding I 25 and thereby cause th closure ofthe switches H9 and HI. The engines will now become synchronizedautomatically at the speed of the master engine B. Subsequently, anysmall changes that may be desirable may be obtained by proper rotationof the'hand wheel I40 of the master engine. To

depressing the button I35. This energizes the solenoids I02 in each ofthe governors and trips the pawls 61 breaking the drive connectionsbetween the step motor drive gears and the speeder adjusters 4. Eachspeeder spring is thus overcome by the associated spring 81, and thespeed adjusters are moved quickly to the speed settings predetermined bythe positions of the stops for the individual speed adjusters.

Restoration of the automatic control is effected by opening the switchI04 as a result of which the pawls 91 reengage the ratchet gears andreestablish the connections between the step motors and the speedadjusters. Then the speeds maybe reduced to the desired value either bychanging the speed setting of the master engine or by engaging thecouplers for simultaneous adjustment of all of the governors.

For many aircraft installations, especially where the ability tomaneuver rapidly is not essenspeeds may be achieved without employing agovernor, the speed adjuster in such a case acting directly on theengine speed controller which may be a fuel throttle, a pitch changer,or the like. A typical modification of this general character is shownin Figs. 8 and 9 wherein the same reference numerals are applied to theparts common to the control v previously described. Two engines B and Care shown, and each is equipped with a servo actuator I48, hydraulicallyoperable in this instance, to change the pitch of the propeller blades6. The actuator I46 is incorporated in and rotates with the propellerassembly which in turn is carried by and rotates with the enginecrankshaft 2| of the prime mover. Through bevel gears I 41," theactuator is adapted to turn the-blades back and forth to a pitchdetermined by the position of the movable member I48 of the controlvalve I49 having lands I50 thereon cooperating with ports in the valvecasing I5I which also rotates with the propeller but is shiftableaxially. The member I48 is movable parallel to the propeller axis, andits projecting end I52 bears against a nonrotatable plate I53 that isshifted back and forth axially in accordance with changes in the axialpositions of the control rack or speed adjuster 4. For this purpose,slots I54 in the plate I53 coact with pins I55 on a ring I56 havingperipheral gear teeth I5'I which mesh with teeth on the'rack 4'. Thepitch adjusting motion of the servo actuator I46 resulting from a changein the position of the rack 4' operates through gears I58 and a pin andslot connection I59 to shift the valve casing I5I relative to thepropeller assembly so that the latter follows up the move- 'ments of thevalve member I48 and interrupts the flow of pressure fluid to or fromthe servo actuator when the propeller blade pitch has been changed \tocorrespond to the changed position of the control rod 4'.

As in the embodiment previously described, the step motor 5| mounted oneach slave engine operates through speed reduction gearing I60 and I6Iand a, normally engaged clutch I 62 to actuate the engine speed adjuster,4. In this case, the clutch is of the friction type having axiallyenacancav ll gageable driving and driven elements I88 and I64, one ofwhich rotates with the armature I85 of a stationary magnet I88. There isa small clearance between the armature and the pole faces of the magnetso that the clutch elements are always brought into firm grippingengagement when the magnet is energized The magnets for both arenormally energized from the battery 11 through the switch I84 which, inthis instance, is connected to the clutch windings throughconductorsifl. When this switch is opened, the speed adjusters 4' ofboth engines move in either direction under the influence of theirsprings.

In some aircraft installations, it isdesirabl'e under special conditionsto move the engine speed adjusters 4' to speed settings short of themaximum and corresponding more nearly to normal cruising speed. To thisend, each of the control racks 4 is urged in the speed-increasingdirection by a compression spring I88 (Figs. 8 and 9) acting against afixed abutment I88. A second compression spring I18 substantiallystronger than the spring I68 acts between the other end of the rack 4and an abutment I which is slidable along an adjustable rod I12 carriedby the other end of the rack. A head I18 on this rod limits the extentof motion of the abutment away from the rack. When the abutment "I isengaging a fixed stop I14 as shown. the control rack is in the desiredcruising speed position. It may be moved by the step motor ii in thespeed-decreasing direction, in which case the rod I12 moves through theabutment I1I further compressing the spring I18. Movement in thespeed-increasing direction results in compression of the spring I88 andmovement of the abutment I1I away from the stop I14. in either directionaway from the position predetermined by the position of the head I18 andthe abutment Hi, the rack will be returned quickly to this positivelydefined position by one of the other springs I88 or I18. Thereafter,reenerigization of the clutch magnet I88 will reestablish the drivingconnection. Such motion of the speed adjuster 4' in either direction tothe predetermined position is made possible with the friction typeclutch shown.

As previously described, the generator III which produces alternatingcurrent the reference frequency in the control shown in Fig. 8 is drivenby a small adjustable speed electric motor H8 which may be locatedconveniently near the control panel H8. The direct current motor shownis of the series type directly coupled to the generator and controlledin a well known manner so as to operate at constant speed. Suchoperation may be obtained by a governor I15 having fly-weights I15carried by a spring I15 on the motor shaft. The governor operatesthrough a pin I18 to actuate a contact I11 cooperating with a contactdisk I18 to form a control switch I19. When the motor II8 exceeds thespeed selected by the switch setting, the switch is opened and aresistance I88 is interposed in the motor circuit. When the speed fallsbelow the selected value, the switch I18 is closed to short-circuit theresistance and speed up the motor.

The speed at which the motor operates may be varied as desired byturning the knob I8I of a screw I82 to change the position of thecontact disk I18. This knob may be on the control panel H3 or in anyother convenient location so that by a simple adjustment, the frequencyof the When the rack is displaced.

generator output may be varied as desired to change the master speed. Inresponse to the current thus generated, the control as a whole operatesin'the same manner as that shown in Fig. 1 to compare the speeds of theslave engines B and C against that of the master power unit and thussynchronize the engines automatically. Thus, the differential motors Hi5and H5 are energized from the master alternator III and also from theslave alternators H4 and 4, the connections being continuous in thisinstance. These differential motors drive the shafts 88 and 88 andthereby actuate the commutator switches 88 and 58 in accordance withdeviations of the slave engine speeds from that of the master motor II8.

The commutating switches 58 are connected to the respective step motors5i and 5I by conductors I88 having interposed therein switches I84 andI88 that are actuated by solenoids I88 and I81 and normally closed asshown when the solenoids are deenergized. Thus, the commutating switchesoperate through the step motors on the slave engines, and as before,actuate the speed adjusters 4 and 4 to synchronize these enginesautomatically at the speed for which the master motor H8 is adjusted tooperate.

Ii desired, electrical means may be provided for enabling the speeds ofthe slave engines B and C to be adjusted manually either individually orcollectively. For this purpose, the solenoids I88 and I81 are firstenergized to disable the automatic control and at the same time closetheir other switches I88 and I88 to disconnect the commutating switches58 and 58* and connect one or both of the step motors 5i and 8I= to anauxiliary commutating switch 58, the connections of the latter beingthrough conductors I88. The latter switch is of the same construction asthe switches 58 and 58 and its shaft 83 may be driven by a separateelectri direct current motor I8I preferably having a permanent magnetstator and reversible by controlling the direction of current flow inits rotor I82. Such energize- -tion is effected by a manually operablereversing switch I83 whose actuator I84 is normally maintained in theneutral position shown. So long as the switch I93 is closed in onedirection or the other, the auxiliary commutator switch 58 is driven andthe step motors 5| operate at higher speed to increase or decrease thespeed settings of the engines.

The energizing circuit for the solenoids I88 and I81 extends from thebattery lead 14 through a switch I88 controlled by a solenoid I81, the

movable contact I88 of a selector switch I88, one or both stationarycontacts 288 and 28I of this switch, conductors 282, the solenoids I88and I81, and the conductor I81 to the other battery lead 18. The contactI88, which is operable manually by turning a knob 288, is wide enough toengage both contacts 288 and 28I in the central position shown. If thespeed of only one engine is to be adjusted, the contact is moved in oneway or the other so as to disengage the contact oi! the engine whosespeed setting is not to be changed.

Energization of the solenoid I81 is controlled by a manually operableswitch 284, closure of which connects the solenoid winding across thepower lines 18 and 14. Such energlzation also opens a switch 285 whichis interposed in conductors 286 that connect the battery lead 14 to onepair of brushes of the commutator switches 88'' and 88. Thus, when theswitch 284 is closed to energize one or both of the solenoids I" and I81and thus disablethe automatic synchronizing control, the power supply toboth commutating switches 59' and 58 is also interrupted therebydisabling the synchronizing control by the commutator switch and stepmotor whose solenoid I88 or I81 may not have been energized because ofthe shifted position of the selector switch I99.

As a result, the automatic synchronizing control is fully disabledirrespective of which engines are to be adjusted in the subsequentoperation of the motor I9I under manual control.

The various manually controlled devices including the actuators for theswtches I8, I04, I93, I 99 and 204 and the master speed adjuster I8Iwould, of course, be arranged compactly on a panel located in theaeroplane cockpit or other convenient place.

speed adjustments independently of the automatic control, that ismechanically with the apparatus shown in Fig. 1 or electrically throughthe motor 'I9I and switch I93 in the control of Fig. 8. Manualadjustments of the engine speeds for various purposes may be madequickly and conveniently and with minimum manipulation Fig. 10 shows astill further modification oi! the synchronizing control that embodies amechanical instead of electrical differential for comparing the speedsof the slave engines with the master speed. In this case, the enginespeed adjusters 4 are actuated as before by step motors 5I and5Icontrolled by commutator switches 58* and 58 which are, however,mounted on and adjacent the associated engine. The shaft 63 of eachswitch is driven through a rotary mechanical connection from theintermediate 208 of a difl'erential gearing 209 one terminal element 2I0 of which is rotated through a direct connection 2 from the associatedslave engine. The other differential terminal 2I2 is driven by asynchronous motor 2I3 also mounted on the engine and energized bycurrent from the master alternator I II so as to run at the selectedreference speed.

With this arrangement, deviation in the speed of either slave enginefrom the master speed will result in turning 01' the intermediate 208 ofthe differential and corresponding rotation of the commutator switch 58to effect the necessary correcting speed adjustment through the stepmotor 5|, the same as in the embodiments previously described.

The synchronizing controls above described possess numerous advantages.For example, due

, to the cogging action produced in the step motors 5| as previouslydescribed, the settings of the engine speed adjusters 4 will bemaintained against the action of the springs 81 in the event of powerfailure at the battery or otherwise. The step motor is particularlyadvantageous in that in synchronizing, its operating speed is proportional to the speed deviation between the master and slave engines sothat it may be stalled at the limits of the speed adjusting rangewithout damage. Moreover, the power input upon such stalling is notchanged; consequently, it is unnecessary to provide limit switches orthe like as in prior synchronizing controls using ordinary electricmotors for speed adjustment.

Because the differential motors II5 merely operate the commutatorswitches 58, they may be of small capacity and light in weight, and thegenerators II I and H4 may be of correspondingly small size and weight.The special speed change effected by breaking the step motor connectionsto the speed adjusters enablesthe synchronizing action to occur at arate sufiiciently slow to permit of accurate speed matching while at thesame time providing a proper safeguard under unusual or specialconditions arising in service operation of the aeroplane. In each of theembodiments disclosed, provision is made for making manual on the partof the pilot. With the controls shown in Figsl and 8, it will beobserved that there are no switches, brushes, slip rings or the like onthe engines or directly subject to the vibration thereof, thiscontributing to trouble free operation of the control. The control shownin Fig. 8 lends itself readily to the maneuvering of an aeroplane bymanipulation of the engine throttles, the individual speed adjusters tnot being influenced by engine speed changes effected by throttlemanipulation.

This application is a continuation in part of my copending applicationSerial No. 426,362, filed January 10, 1942, now abandoned.

I claim as my invention:

1. A control for synchronizing a plurality of power units having, incombination, adjusters controlling the speeds of the respective unitsand each having a member variably movable to change the speed setting,reversible electric motors each having a disengageable drivingconnection with one of said members, means associated with therespective members for biasing the speed control member to apredetermined position when the associated driving connection is broken,electromagnetic means controlling the engagement and disengagement ofsaid connections, mechanism automatically responsive to the speeds ofsaid units and controlling the operation of at least one of said motorsto synchronize the units, and means separate-from said mechanism andoperable at will to control the energization of said electromagneticmeans and permit said mechanism to be disabled and the speed settings ofsaid members to be changed quickly by the action of said biasing-means.

2., A control for synchronizing a plurality of power units having, incombination, devices selectively adjustable to vary the speeds of therespective units, mechanism responsive to speed changes of said unitsand operable to adjust one of said devices and synchronize said unitsautomatically, means associated with the respective devices and normallytending to change the speed setting thereof to a predetermined value,and manually controllable means for rendering each of said lastmentioned means operative to permit the speed settings of all of saiddevices to be changed quickly to said predetermined value. I

3. A control for synchronizing a plurality of power units having, incombination, adjusters controlling the speeds of the respective unitsand each having a member variably movable to change the speed setting ofthe associated unit, reversible electric motors each having adisengageable driving connection with one of said members, meanassociated with the respective adjusters for biasing the speed controlmember to a predetermined position when the associated drivingconnection is broken, electromagautomatically, and manually controllableswitch means located at a point of control remote from said power unitsand operable to control the energizrtion of said electromagnets.

a. A speed control for a plurality of prime movers having, incombination, individual selectively operable adjusters governing thespeed of the respective prime movers, individual means biasing therespective adjusters to predetermined speed settings, reversibleelectric motors each having stator and rotor members and a winding andoperable to overcome said biasing means and drive one of said adjustersin opposite directions according to the selective energization of thewinding, one of said members being permanently magnetized and attractingthe other member to hold the position of the associated acfiusteragainst the biasing means when said motor winding is deenergized,mechanism for controlling the selective energization of said motorwindings, and means operable selectively to disable said motors andpermit actuation of the associated adjusters by said biasing means.

5. In a control of the character described, the combination of, a speedcontrol member variably movable to different speed settings, areversible power actuator, a driving connection including diiierentialgearing having a driven intermediate element connected to said memberand two terminal elements, one driven by said actuator, an annularseries of teeth movable with said other terminal element, a manuallycontrollable pawl engageable with said teeth and normally acting to holdthe teeth against movement but releasable to free the second terminalelement, and biasing means urging said member to a predeterminedposition and operable to move the member to such position when saidsecond terminal element is released.

6. In a control of the character described, the combination of, a speedcontrol member variably movable to different speed settings, biasingmean urging said member to a predetermined position, a reversible poweractuator, speed reducing gearing driven thereby, means providing adisengageable driving connection between said gearing and said memberincluding a normally stationary rotary element releasable to free saidmember for movement by said biasing means and carrying an annular seriesof teeth, a latch engageable with said teeth and normally acting to holdsaid element against turning, and an electromagnet controlling themovement of said latch between active and inactive positions.

7. In a control of the character described, the combination of, a speedcontrol member variably movable to different speed settings, biasingmeans urging said member to a predetermined position, a reversible poweractuator, speed reducing gearing driven thereby, means providing adisengageable driving connection between said gearing and said memberincluding a normally engaged clutch adapted when released to free saidmember for movement by said biasing means, and manually controllablemeans governing the engagement and disengagement of said clutch. Y

8, Mechanism for controlling the speed of a prime mover having, incombination, a speed adjusting member selectively movable to differentsettings corresponding to' speeds desired to be maintained, energystoring means normally biasing said member to a predetermined setting, areversible electric motor, means providing a disengageable drivingconnection between said motor and said member and operable by the motorto overcome the biasing means and move said member to said predeterminedsetting at a limited rate substantially slower than the rate of movementthereof by said biasing means, mechanism for controlling said motorselectively to adjust the setting of said member at said limited rate,and selectively operable electromagnetic means controlling theengagement and disengagement of said driving connection, said energystoring means actuating said member to said predetermined setting upondisengagement of said connection by said electromagnetic means.

9. A control for matching the speed of a controlled power unit with thatof a master unit having, in combination, an adjuster associated withsaid controlled unit and selectively operable to determine the speedthereof automatically in accordance with the adjuster setting, anelectric motor having a stator element with a plurality of windings anda rotor element rotat able in response to energization of said windingsin different polarity combinations, a speed reducing driving connectionbetween said rotor element and said adjuster operable to vary the speedsetting thereof, a source of direct current, a switch located at a pointof control remote from said units and operable in different angularpositions of its movable member to connect the terminals of said currentsource to said windings in different combinations and causespeed-increasing or speed-decreasing rotation of said rotor element asdetermined by the direction of movement of said member, and means actingdifferentially in response to deviation in the speed of said controlledunit from that of the master unit to actuate said switch and cause saidrotor element to turn in a direction to correct for such deviation, oneof said motor elements being permanently magnetized and coasting withthe other element to produce a cogging action capable of maintaining thespeed setting ofsaid adjuster when all of said stator windings aredeenergized.

10. A control for matching the speed of a controlled power unit withthat of a master unit having, in combination, an adjuster associatedwith said controlled unit and selectively operable to determine thespeed thereof, an electric motor having a stator with a plurality ofwindings and a rotor operable in response to energization of saidwindings in difierent polarity combinations, a driving connectionbetween said rotor and said adjuster operable to vary the speed settingthereof, a source of direct current, a switch having an angularlymovable member and operable in a multiplicity of different angularpositions of said member to connect the terminals of said current sourceto said windings in different polarity combinations and causespeedincreasing .or speed-decreasing rotation of said rotor asdetermined by the direction of movement of said member, a differentialmotor arranged to turn said movable switch member and having windings,and electric generators respectively driven by said master andcontrolled units and arranged to energize the respective windings ofsaid differential motor and cause said switch member to turn in adirection and at a speed determined by the speed difference between themaster and controlled units.

11. A control for matching the speed of a controlled power unit withthat of a master unit having, in combination, an adjuster associatedwith said controlled unit and operable to control the speed thereofaccording to the position of the adjuster, an electric motor operablewith a stepthereof in response to movements of the movable member of theswitch-in opposite directions, a

differential motor arranged to actuate said movable switch member andhaving windings, and electric generators respectively driven by saidmaster and controllable units and arranged to energize the respectivewindings of said differential motor and cause said switch member to turnin a direction and at a speed determined by the speed diiierence betweenthe master and controlled units.

12. Mechanism for controlling the speed of a prime mover having, incombination, a speed adjusting member selectively movable to differentsettings corresponding to speeds desired to be maintained, an electricmotor including a stator element and a rotor element one having aplurality of windings energizable in difl'erent polarity combinations toturn the rotor element, a driving connection between said rotor elementand said member including a selectively engageable and disengageableclutch, a source of direct current, a switch having a movable part andoperable in different angular positions of the part to connect theterminals of said current source to said windings in difierentcombinations and cause corresponding speed-increasing or speeddecreasingrotation of said rotor element when said clutch is engaged, energystoring means normally biasing said member to a predetermined settingand operable to move the member when said clutch is disengaged, saidbiasing means being overcome by said motor when said clutch is engaged,mechanism for turning said switch part selectively to adjust the settingof said member, and electromagnetic means controlling the engagement anddisengagement of said clutch.

l3. Mechanism for controlling the speed of a prime mover having, incombination, a speed adlusting member selectively movable to difierentsettings within a range of speeds desired to be maintained, energystoring means normally biasing said member selectively in one directionor the other toward a predetermined intermediate setting within saidrange, a reversible electric motor having a rotary drivingconnectionwith said member and capable of overcoming the biasing meansthereof, said connection including a clutch having coacting rotaryelements engageable frictionally in all relative angular positions ofthe two elements, mechanism for controlling said motor selectively toadjust the setting of said member, and electromagnetic means controlling18 to adjust the position of said member, means normally maintainingsaid driving connection effective, and electromagnetic means normallymaintained deenergized and adapted when energized to overcome saidmaintaining means and release said driving connection whereby to rendersaid energy storing means effective to move said adjusting member tosaid predetermined position.

15. A control 101' synchronizing the operation of master and slave powerunits having, in combination, devices individually adjustable to varythe operating speeds of the respective units, individual power actuatorsfor the respective devices selectiveiy operable under control from aremote point, positive stops for limiting the motions of the respectivespeed adjusting devices by their actuators in the speed-increasingdirection and each adjustable individually to determine the limit speedsetting of its associated device, means at said remote point operableselectively to energize the actuators of said master unit and adjust thespeed setting oi the associated device, means operable to compare thespeedsoi' the master and slave power units and energize the actuator ofthe slave unit to maintain the slave and master units synchronized, andsupplemental control means at said remote point operable to activate allof said actuators simultaneously and cause movement of all of the speedadjusting devices in the speedincreasing direction to limit positionsdetermined by said stops whereby to bring all of said units tocorresponding speeds.

16. A control for synchronizing the operation of master and slave powerunits having, in combination, devices individually and selectivelyadjustable to vary the speeds of the respective units. mechanismresponsive to speed changes of said power-units and operable tosynchronize said units automatically, stops for positively limiting themotions of the respective speed adjusting devices in thespeed-increasing direction, and means manuaily controllable and operableto override said mechanism and cause movement of all of the speedadjusting devices in the speed-increasing direction until each deviceencounters its limit 1 stop whereby all 01' said devices are brought tocorresponding speed settings.

17. A control for synchronizing the operation of master and slave powerunits having, in combination, devices individually adjustable to varythe speeds of the respective power units, individual power actuators forthe respective devices selectively operable under control from a remotepoint, automatically acting control means operable to compare the speedsof the master and slave units and energize the actuator of theislaveunit to maintain the slave and master units synchronized,

the operation of said clutch, said energy storing I means actingselectively upon release of said clutch to move said member to saidintermediate position,

4. Mechanism for controlling the speed of a prime mover having, incombination, a speed adjusting member selectively movable to differentpositions, energy storing means normally biasing said member to apredetermined position, a reversible electric motor, means providing areleasable driving connection between said motor and said member andoperable by the motor, when engaged, to overcome the biasing means andmove said member to said predetermined position at a rate substantiallyslower than the rate of movement thereof by said biasing means,mechanism for controlling said motor selectively supplemental meanscontrollable electrically from said remote point and operable toactivate all of said actuators simultaneously and cause movement of allof the speed adjusting devices in the speed-increasing direction, andmeans for limiting the last mentioned speed-increasing motion of saiddevices to a common speed setting.

18. A control for matching the speed of a controlled power unit withthat of a master unit having, in combination, an adjuster adapted to beassociated with said controlled unit for varyin the speed thereofaccording to the speed of the adjuster, a direct current motor having arotary rotor element and a plurality of windings energizable indifl'erent polarity combinations to turn said rotor through amultiplicity of steps in each revolution, a switch electricallyconnected to said REFERENCES CITED The following references are ofrecord in the file of this patent:

Number UNITED STATES PATENTS Name Date Btaeae Sept. 15, 1925 Lenehan May'I, 1940 Kaila June 18, 1940 Martin Aug. 12, 1941 Martin Oct. 7, 1941Taylor Dec. 2, 1941 Day Dec. 2, 1941 Drake Aug. 24, 1943

